Buggy code:
public class VariablesEvaluator extends Evaluator implements EvaluationConstants { int startPosOffset = 0 ; VariablesEvaluator ( EvaluationContext context , INameEnvironment environment , Map options , IRequestor requestor , IProblemFactory problemFactory ) { } protected void addEvaluationResultForCompilationProblem ( Map resultsByIDs , IProblem problem , char [ ] cuSource ) { } protected char [ ] getClassName ( ) { } Compiler getCompiler ( ICompilerRequestor compilerRequestor ) { } protected char [ ] getPackageName ( ) { } protected char [ ] getSource ( ) { StringBuffer buffer = new StringBuffer ( ) ; int lineNumberOffset = 1 ; char [ ] packageName = getPackageName ( ) ; if ( ( packageName . length ) != 0 ) { buffer . append ( "package<seq2seq4repair_space>" ) ; buffer . append ( packageName ) ; buffer . append ( ';' ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; } char [ ] [ ] imports = this . context . imports ; for ( int i = 0 ; i < ( imports . length ) ; i ++ ) { buffer . append ( "import<seq2seq4repair_space>" ) ; buffer . append ( imports [ i ] ) ; buffer . append ( ';' ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; } buffer . append ( "public<seq2seq4repair_space>class<seq2seq4repair_space>" ) ; buffer . append ( getClassName ( ) ) ; buffer . append ( "<seq2seq4repair_space>extends<seq2seq4repair_space>" ) ; buffer . append ( EvaluationConstants . PACKAGE_NAME ) ; buffer . append ( "." ) ; buffer . append ( EvaluationConstants . ROOT_CLASS_NAME ) ; buffer . append ( "<seq2seq4repair_space>{" ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; <START_BUG> startPosOffset = buffer . length ( ) ; <END_BUG> GlobalVariable [ ] vars = this . context . variables ; VariablesInfo installedVars = this . context . installedVars ; for ( int i = 0 ; i < ( this . context . variableCount ) ; i ++ ) { GlobalVariable var = vars [ i ] ; buffer . append ( "\tpublic<seq2seq4repair_space>static<seq2seq4repair_space>" ) ; var . declarationStart = buffer . length ( ) ; buffer . append ( var . typeName ) ; buffer . append ( "<seq2seq4repair_space>" ) ; char [ ] varName = var . name ; buffer . append ( varName ) ; buffer . append ( ';' ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; } buffer . append ( "\tstatic<seq2seq4repair_space>{" ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; for ( int i = 0 ; i < ( this . context . variableCount ) ; i ++ ) { GlobalVariable var = vars [ i ] ; char [ ] varName = var . name ; GlobalVariable installedVar = ( installedVars == null ) ? null : installedVars . varNamed ( varName ) ; if ( ( installedVar == null ) || ( ! ( CharOperation . equals ( installedVar . typeName , var . typeName ) ) ) ) { char [ ] initializer = var . initializer ; if ( initializer != null ) { buffer . append ( "\t\ttry<seq2seq4repair_space>{" ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; var . initializerLineStart = lineNumberOffset ; buffer . append ( "\t\t\t" ) ; var . initializerStart = buffer . length ( ) ; buffer . append ( varName ) ; buffer . append ( "=<seq2seq4repair_space>" ) ; var . initExpressionStart = buffer . length ( ) ; buffer . append ( initializer ) ; lineNumberOffset += numberOfCRs ( initializer ) ; buffer . append ( ';' ) . append ( Util . LINE_SEPARATOR ) ; buffer . append ( "\t\t}<seq2seq4repair_space>catch<seq2seq4repair_space>(Throwable<seq2seq4repair_space>e)<seq2seq4repair_space>{" ) . append ( Util . LINE_SEPARATOR ) ; buffer . append ( "\t\t\te.printStackTrace();" ) . append ( Util . LINE_SEPARATOR ) ; buffer . append ( "\t\t}" ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset += 4 ; } } else { buffer . append ( "\t\t" ) ; buffer . append ( varName ) ; buffer . append ( "=<seq2seq4repair_space>" ) ; char [ ] installedPackageName = installedVars . packageName ; if ( ( installedPackageName != null ) && ( ( installedPackageName . length ) != 0 ) ) { buffer . append ( installedPackageName ) ; buffer . append ( "." ) ; } buffer . append ( installedVars . className ) ; buffer . append ( "." ) ; buffer . append ( varName ) ; buffer . append ( ';' ) . append ( Util . LINE_SEPARATOR ) ; lineNumberOffset ++ ; } } buffer . append ( "\t}" ) . append ( Util . LINE_SEPARATOR ) ; buffer . append ( '}' ) . append ( Util . LINE_SEPARATOR ) ; int length = buffer . length ( ) ; char [ ] result = new char [ length ] ; buffer . getChars ( 0 , length , result , 0 ) ; return result ; } private int numberOfCRs ( char [ ] source ) { } }

Fix:
this . startPosOffset = buffer . length ( ) ;